Question

Suppose that each object in an n-object list L is colored either red or blue. Give an efficient EREW algorithm to form two lists from the objects in L: one consisting of the blue objects and one consisting of the red objects.

Answer 1

class MyObj {

    Property a;
    Property b;
    Property c;

    public boolean equals(Object o) {
        // use == if Property is primitive, like int or something
        return o instanceof MyObj && a.equals(o.a) && b.equals(o.b) && c.equals(o.c);
    }

    // edit - when you override equals, also override hashcode
    public int hashCode() {
        return a.hashCode() ^ b.hashCode() ^ c.hashCode();
    }

    public String toString() {
        return a.toString() + " " + b.toString() + " " + c.toString();
    }

}

// later in your main method
Set<MyObj> objSet = new HashSet<MyObj>();
for(MyObj o : list1) objSet.add(o);
for(MyObj o : list2) if(objSet.contains(o)) System.out.println(o + " is a match!");